The B4594 is a cross-country road, mostly in south Radnorshire. It was unclassified for many years but gained its number in the 1960s.
The road starts on the A470 west of Erwood. It heads northeast and crosses the River Wye immediately before zigzagging to go under a low, narrow bridge under a dismantled railway line. On the far side the road bears round to the left and becomes the B4567, the original number of the section just gone, whilst the B4594 TOTSOs right.
Continuing northeastwards we climb steeply out of the valley via a couple of hairpin bends and then a straighter section. At the top of the hill are a farm and a chapel, after which we descend again into the next valley. The road narrows unexpectedly at a crossroads and then we follow the valley of the Bachawy upstream past Llanbedr after which the road widens as we approach Painscastle. There's a sharp left-hand bend in the village centre, then the road becomes even narrower than before as we reenter open country, although it soon widens out again.
We continue up the valley to Rhos-goch then go over a ridge to reach the next valley, that of the Cwmilsa Brook. This is narrower than the last valley so we run halfway up the valley side and the road narrows to fit in. We descend into Newchurch, where we bear left immediately in front of the church. The road widens and crosses the River Arrow, then climbs steeply back into the hills; the central line soon goes again but only briefly. After reaching a summit we descend gently into Gladestry. We zigzag through the village and head straight towards the edge of Hergest Ridge before bearing left to run round the side. We pass a few striking hills then reach a stretch of flat land at Dolyhir.
We run along this flat land to the south of Old Radnor Hill. Soon we join the trackbed of an old railway line (the old road zigzagged left through Burlingjobb). After passing through the site of Stanner Halt (where we pass what looks like a former railway building) the road ends at a T junction on the A44.